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Show revealed that the predicted sulphur capture increased with both increased SO2 concentration (or coal sulphur content) and increased Ca/S. The predicted sulphur capture was still within the range of values measured in the Saskatchewan Power experimental tests. In these tests sulphur captures of 14 to 3 0 % were measured for 0.5 w t % sulphur coal and Ca/S of 2.0, firing a similar low sulphur coal (CEA Report No. 532 G 546, 1987) Table 3 - Sorbent Injection Modelling Results Coal Sulphur (wt%) 0.25 0.25 0.5 1.0 Ca/S (molar ra 2.0 4.0 2.0 2.0 tio) S Capture (%) 16 28 23 34 Visualization of the results of the predicted flow and temperature fields in the boiler is shown in Figures 2 through 11. Figure 2 shows the velocity profiles on the inlet and outlet planes of the boiler. This figure demonstrates the significant three-dimensional nature of the internal flow. Figure 3 shows sulphur dioxide (SO2) concentration distribution at the inlet and outlet plane. The non-uniformity of the composition is evident and it persists through to the outlet plane, though the mixing in the heat exchanger bundles has significantly reduced the magnitude of the variation at the outlet. The colored planes in Figure 4 shows the predicted sorbent particle concentration distribution at the inlet, inlet to the cross-over, and outlet planes for the swirling inlet simulations. As would be expected, the particles tended to migrate to the outer walls of the boiler due to the swirl, as well as, the turning of the flow in the cross-over section. Figure 5 shows some representative calculated particle tracks superimposed onto Figure 4. The movement and concentration of particles as they move through the boiler could be of importance if simulations of boiler erosion patterns were performed, as they indicate the importance of simulating the full three dimensional nature of the flow, as well as, the three dimensional geometry in the boiler. Figure 5 shows the time-temperature history of representative sorbent particles. As can be seen in Figure 5, the particles reached the outlet plane (temperatures below approximately 980 K or about 700 °C) in about 0.9 to 1.2 seconds from injection. This was in the range of expected particle residence times on a full-scale boiler. In these simulations the ash loading in the boiler (from Table 1) was approximately 4.69 kg/s or about 6.76 T/d. The use of sorbent injection, at a Ca/S of 2.0, for sulphur dioxide control in the combustion of Highvale coal would result in a boiler ash loading increase of about 0.316 kg/s, or an increase in the boiler ash loading of approximately 6.7%. |
